# Show postscript point versus Anglo-Saxon point

I am doing a practical job comparing the postscript point (1/72) with the Anglo-Saxon point (1/72.27). I need help to be able to show the difference in size in a character (it is indistinct of which). The idea is to show the difference not with a rule, but with two overlapping characters (one on top of the other). Thanks for the help

The visual difference is small:

\documentclass[landscape]{article}

\usepackage{graphicx}
\usepackage{calc}

\newlength\charheight

\begin{document}
\settoheight\charheight{\Huge X}
\setlength\charheight{\charheight*\ratio{72.27pt}{72pt}}

pt$\rightarrow$\scalebox{10}{\Huge X\resizebox{!}{\charheight}{X}}$\leftarrow$bp
\end{document}


Here is a solution (the difference is very small...).

\documentclass[tikz,margin=0mm]{standalone}
\usepackage{lmodern}
\begin{document}
\begin{tikzpicture}[inner sep=0]
\begin{scope}[blend group=difference]
\node[font=\fontsize{52pt}{52pt}\selectfont]{A};
\node[font=\fontsize{52bp}{52bp}\selectfont,text=white]{A};
\end{scope}
\end{tikzpicture}
\end{document}


Here is a south west anchored variant:

\documentclass[tikz,margin=0mm]{standalone}
\usepackage{lmodern}
\begin{document}
\begin{tikzpicture}[inner sep=0]
\begin{scope}[blend group=difference]
\node[anchor=south west,font=\fontsize{52pt}{52pt}\selectfont]{A};
\node[anchor=south west,font=\fontsize{52bp}{52bp}\selectfont,text=white]{A};
\end{scope}
\end{tikzpicture}
\end{document}


• Thanks Paul, your example is what I need, but the characters should not be centered, but anchored at a point equivalent to 0 of an x ​​and y coordinate, to correctly dimension the difference. Is it possible with is code? – Imago Mundi Sep 19 '19 at 14:37
• @ImagoMundi You can add the anchor=south east key to each node... – Paul Gaborit Sep 19 '19 at 15:03
• Thanks Paul, it's exactly what I was looking for. My practical work is based on showing that this small difference added to 800,000 characters (for example a 320-page book) plus the efficiency of the TeX engine in typographical calculations, make a big difference. – Imago Mundi Sep 19 '19 at 23:23

If I compile

\font\PT=ptmr at 1000pt
\font\BP=ptmr at 1000bp

\setbox0=\hbox{\PT A}\showthe\ht0
\setbox0=\hbox{\BP A}\showthe\ht0

\bye


I get on the console

> 673.00034pt.
l.4 \setbox0=\hbox{\PT A}\showthe\ht0

?
> 675.52408pt.
l.5 \setbox0=\hbox{\BP A}\showthe\ht0

?


which means that the difference in height is about 2.5pt, less than one 1mm. At 100pt/100bp, the difference is less than 0.1mm.

You're not going to see any difference at standard sizes (and TeX doesn't load fonts at different sizes if the gap is very small).

Here's the picture I get by printing a black 1000bp A under a red 1000pt A, at 2400% (just the top).

At 100% magnification on a Retina display,